The Heros of Olympus Series By Rick Riordan

The Lost Hero
Jason has a problem. He can't remember anything. Apparently he has a girlfriend named Piper and a best friend named Leo.
Piper has a secret. Her father a famous actor has been missing for three days and she doen't understand why her boyfriend wakes up from a nap and doesn't remember her.
Leo has a way with tools. Apparently, he is related to Hepheastus, the god of metal and forges. Does this have to do with Jason's amneisa or the fact that he keeps seeing ghosts?

The Son of Neptune
Percy is Confused. When he woke up, he didn't know anything accept his name. The only thing he can recall from his past is another name: Annabeth.
Hazel is supposed to be dead. When she lived before, she didn't do a very good job. She almost unleashed the most powerful giant. Now, the future of the world is at risk, because of her. She wishes she could ride away on  the stallion that appears in her dreams.
Frank is a klutz. His grandmother says he can be anything he wants to be, but he doesn't see it. He feels so bulky, especially in front of Hazel, his closest friend, maybe even close enough to tell her secret.